The continuous trend in the development of electronic devices has been to minimize the sizes of the devices. While the current generation of commercial microelectronics are based on sub-micron design rules, significant research and development efforts are directed towards exploring devices on the nano-scale, with the dimensions of the devices often measured in nanometers or tens of nanometers. Besides the significant reduction of individual device size and much higher packing density compared to microscale devices, nanoscale devices may also provide new functionalities due to physical phenomena on the nanoscale that are not observed on the microscale.
For instance, electronic switching in nanoscale devices using titanium oxide as the switching material has recently been reported. The resistive switching behavior of such a device has been linked to the memristor circuit element theory originally predicted in 1971 by L. O. Chua. The discovery of the memristive behavior in the nanoscale switch has generated significant interest, and there are substantial on-going research efforts to further develop such nanoscale switches and to implement them in various applications. One of the many important potential applications is to use such a switching device as a memory unit to store digital data.
The devices recently reported using titanium oxide (and other oxides) typically have involved two oxide phases (TiO2 and an oxygen-deficient phase, TiO2-x). The two oxide phases (or one oxide phase, TiO2, bounded by two oxide phases, TiO2-x) are contacted by metal electrodes, typically, Pt, Ru, W, or other suitable metals.
In such metal/oxide/metal memristive junctions, the electrode materials usually tend to reduce the switching materials and induce some oxygen vacancies at the metal/oxide interface, which is the crucial region for switching and needs to be well-controlled.